In general, semiconductor memory devices such as double data rate synchronous dynamic random access memory (DDR SDRAM) devices are characterized by various alternating current (AC) parameter specifications for guaranteeing allowable margins in data transmission. The AC parameters of the semiconductor memory devices may include ‘tAC’, ‘tDQSCK’ and ‘tDQSS’. The AC parameter ‘tAC’ has a relationship between a clock signal and data signals, the AC parameter ‘tDQSCK’ has a relationship between the clock signal and data strobe signals, and the AC parameter ‘tDQSS’ has a relationship between the data signals and the data strobe signals.
In more detail, the AC parameter ‘tDQSCK’ may relate to a skew between external clock signals and data strobe signals. If the AC parameter ‘tDQSCK’ is out of an allowable range, the semiconductor memory devices may malfunction during a read operation. Accordingly, after the semiconductor memory devices are fabricated and/or packaged, the semiconductor memory devices may be evaluated or tested to measure the AC parameters.